Measurement of local temperature increments induced by cultured HepG2 cells with micro-thermocouples in a thermally stabilized system

Abstract

To monitor the temperature distribution of a cell and its changes under varied conditions is currently a technical challenge. A variety of non-contact methods used for measuring cellular temperature have been developed, where changes of local temperature at cell-level and sub-cell-level are indirectly calculated through the changes in intensity, band-shape, bandwidth, lifetime or polarization anisotropy of the fluorescence spectra recorded from the nano-sized fluorescent materials pre-injected into the target cell. Unfortunately, the optical properties of the fluorescent nano-materials may be affected by complicated intracellular environment, leading to unexpected measurement errors and controversial arguments. Here, we attempted to offer an alternative approach for measuring the absolute increments of local temperature in micro-Testing Zones induced by live cells. In this method, built-in high-performance micro-thermocouple arrays and double-stabilized system with a stability of 10 mK were applied. Increments of local temperature close to adherent human hepatoblastoma (HepG2) cells were continuously recorded for days without stimulus, showing frequent fluctuations within 60 mK and a maximum increment by 285 mK. This method may open a door for real-time recording of the absolute local temperature increments of individual cells, therefore offering valuable information for cell biology and clinical therapy in the field of cancer research.

The challenge of intracellular temperature

“…Two more recent studies using microfabricated thermocouples also report a temperature increase in individual cells, one in relatively longer (Yang et al 2017) and the other on shorter time scales (Rajagopal et al 2019). The approach by Yang et al was to build their high-performance micro-thermocouple arrays, over which adherent cells were cultured, within a double-stabilized tent (Yang et al 2017). Their thermally stabilized system enabled measurements in individual adherent human hepatoblastoma cells in unstimulated conditions for days.…”

Thermophoretic Micron-Scale Devices: Practical Approach and Review

“…The accuracy of a thermocouple of is one order of magnitude better than for RTDs and the actual voltage measurement is straightforward. Additionally, using cleanroom facilities, it is possible to reduce the size of the junction (measuring point) to 0.1 m [ 105 , 106 , 107 ]. However, the voltage level is rather low, so that external electric fields can induce some noise.…”

Thermal sensing in fluid at the micro-nano-scales

“…Cell temperature measurement is recently a hot research field in which various thermometers have been employed to measure cellular temperature on cell membrane, 93 in cytoplasm, 91 and on organelles. 169,170 Temperature is such an important parameter that influences cell activities.…”

“…Therefore, our group attempted to measure the local temperature increments induced by cultured HepG2 cells with micro-TFTCs. 93 In this work, the Pd/Cr or Cr/Pt TFTCs with thermopowers of 20.99 6 0.1 lV/K and 15.59 6 0.3 lV/K were fabricated. Figure 11(a) presents the fabrication processes of the key elements of the cell temperature measurement device.…”